Method for replacing a damaged spinal disc

ABSTRACT

A method for replacing a damaged spinal disc between first and second vertebrae of a spinal column includes connecting a first mounting member with the first vertebra of the spinal column. An artificial disc is moved between the first and second vertebrae and into engagement with the first mounting member to guide the artificial disc into position between the first and second vertebrae. The artificial disc includes a resilient core having a first surface and a second surface, a first retaining member connected to the first surface of the resilient core, and a second retaining member connected to the second surface of the resilient core. The first retaining member has an outer surface engageable with a first vertebra of the spinal column and an inner surface facing the first surface of the resilient core. The second retaining member has an outer surface engageable with the second vertebra of the spinal column and an inner surface facing the second surface of the resilient core.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for replacinga damaged spinal disc in a spinal column, and more specifically, to anapparatus having a resilient core for replacing a damaged spinal disc ina spinal column.

BACKGROUND OF THE INVENTION

A known artificial disc member is disclosed in U.S. Pat. Nos. 5,370,697.5,370,697 discloses an artificial disc having upper and lower supportsconnected to adjacent vertebrae and an elastic separator. The separatorhas cover plates connected to opposite sides of an elastic core. Theseparator is a separate insert part that may be inserted between theupper and lower supports after the supports are connected to thevertebrae. The separator does not engage the vertebrae.

SUMMARY OF THE INVENTION

A method for replacing a damaged spinal disc between first and secondvertebrae of a spinal column includes connecting a first mounting memberwith the first vertebra of the spinal column. An artificial disc ismoved between the first and second vertebrae and into engagement withthe first mounting member to guide the artificial disc into positionbetween the first and second vertebrae. The artificial disc includes aresilient core having a first surface and a second surface, a firstretaining member connected to the first surface of the resilient core,and a second retaining member connected to the second surface of theresilient core. The first retaining member has an outer surfaceengageable with a first vertebra of the spinal column and an innersurface facing the first surface of the resilient core. The secondretaining member has an outer surface engageable with the secondvertebra of the spinal column and an inner surface facing the secondsurface of the resilient core.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present invention will becomeapparent to one skilled in the art to which the present inventionrelates upon consideration of the following description of the inventionwith reference to the accompanying drawings, in which:

FIG. 1 is a pictorial view of an apparatus to replace a damaged spinaldisc constructed in accordance with the present invention;

FIG. 2 is a sectional view of the apparatus of FIG. 1;

FIG. 3 is a pictorial view of an artificial disc of the apparatus ofFIG. 1

FIG. 4 is a schematic top view of the artificial disc of FIG. 3;

FIG. 5 is a pictorial view of a mounting member of the apparatus of FIG.1;

FIG. 6 is a schematic sectional view of the apparatus of FIG. 1 betweenadjacent vertebrae of a human spinal column;

FIG. 7 is a schematic sectional view of the apparatus of FIG. 1 betweenadjacent vertebrae of the spinal column showing the spinal column incompression;

FIG. 8 is a schematic side view of an actuator for use in connectingmounting members shown in FIG. 5 to adjacent vertebrae;

FIG. 9 is a pictorial view of insertion members for use with theactuator of FIG. 8 to connect the mounting members to adjacent vertebraeof the spinal column;

FIG. 10 is a pictorial view of one of the insertion members of FIG. 9;

FIG. 11 is a schematic side view of the insertion member of FIG. 10;

FIG. 12 is a schematic top view of the insertion member of FIG. 10;

FIG. 13 is a sectional view of a portion of the insertion member takenalong the line 13-13 in FIG. 12;

FIG. 14 is a pictorial view of a slider connectable to one of theinsertion members of FIG. 9;

FIG. 15 is a pictorial view of a spring member for connecting themounting member to one of the insertion members of FIG. 9;

FIG. 16 is a pictorial view of a surgical tool for use in inserting theartificial disc of FIG. 2 between the adjacent vertebrae; and

FIG. 17 is an enlarged view of a portion of the surgical tool of FIG.16.

DESCRIPTION OF THE INVENTION

The present invention relates to an apparatus or prosthesis to replace adamaged or degenerated spinal disc in a spinal column of a human. FIGS.1-7 illustrate an apparatus or prosthesis 10 to replace a damaged ordegenerated spinal disc in a spinal column. The apparatus 10 (FIG. 6) isused to replace a damaged spinal disc between adjacent upper and lowervertebrae 12 and 14 of a human spinal column 16. The apparatus 10 (FIGS.1-7) includes an artificial disc 18 and mounting members 100 that helpconnect the disc 18 to the adjacent vertebrae 12 and 14. The mountingmembers 100 also help position the disc 18 relative to the vertebrae 12and 14.

The apparatus 10 (FIG. 1) includes an upper or first retaining device20, a lower or second retaining device 60 and a resilient core 90interposed between and adhered to the retaining devices. The upper andlower retaining devices 20 and 60 are identical to each other andinclude mounting members 100. The apparatus 10 is symmetrical about ahorizontally extending plane A (FIG. 3). The terms “upper” and “lower”are used herein with reference to the orientation of the apparatus 10when in the human body, as illustrated in FIG. 6, to distinguish the twoidentical retaining devices for reference purposes.

The upper retaining device 20 includes an upper or first retaining ringor member 21 and a mounting member 100. The artificial disc 18 includesthe upper retaining member 21. The upper retaining member 21 is rigidand made of a biocompatible material such as a biocompatible metal orpolymer. It is contemplated that the upper retaining member 21 could bemade of a titanium alloy. The upper retaining member 21 has an outersurface 22 engageable with the vertebra 12. An inner concave surface 24of the upper retaining member 21 is affixed or bonded to the resilientcore 90. It is contemplated that the inner surface 24 may have beads(not shown) sintered on the inner surface or a texture (not shown)etched onto the inner surface to help connect the upper retaining member21 to the core 90.

A plurality of guides or ribs 26 (FIGS. 3-4) and a central rib 28 extendfrom the outer surface 22. Although the upper retaining member 21 isshown as having four ribs 26, it is contemplated that the upperretaining member may have any number of ribs 26. The ribs 26 engage thevertebra 12, as shown in FIGS. 6-7, to retain the apparatus 10 inposition between the vertebrae 12 and 14. The outer surface 22 may alsohave beads (not shown) sintered on the outer surface or a texture (notshown) etched onto the outer surface to further retain the apparatus 10between the vertebrae 12 and 14.

The ribs 26 (FIGS. 1-4) extend generally parallel to each other from aproximal side 30 of the disc 18 to an anterior side 32 of the disc. Thecentral rib 28 extends from the anterior side 32 of the disc 18 to anaxially extending circular opening 36 in the upper retaining member 21.It is contemplated that the ribs 26 and 28 may extend in any desireddirection. The direction in which the ribs 26 and 28 extend isdetermined by the direction of insertion of the disc 18.

The axially extending opening 36 (FIGS. 2-4) extends through the outersurface 22 and the inner surface 24 of the upper retaining member 21.The upper retaining member 21 has a frustoconical surface 37 at leastpartially defining the opening 36. An upper portion of the opening 36has a first diameter and a lower portion of the opening has a seconddiameter smaller than the first diameter. The opening 36 is centrallylocated between two of the ribs 26. Accordingly, there is no ribextending from the proximal side 30 of the disc 18 to the opening 36.Although the opening 36 is shown as being circular, it is contemplatedthat the opening may have any desired shape.

A flange portion 38 extends from the upper retaining member 21 on theanterior side 32 of the disc 18. The flange portion 38 has a recess 40adjacent the central rib 28. The recess 40 is defined by a bottomsurface 42 and side surfaces 44 and 46 extending upwardly from thebottom surface 42. An oval shaped slot 48 extends through the bottomsurface 42 of the flange portion 38. The slot 48 extends in a directiontransverse to the direction in which the rib 28 extends.

The inner concave surface 24 (FIG. 2) of the upper retaining member 21is affixed or bonded to the resilient core 90. The upper retainingmember 21 includes a peripheral flange portion 50 extending toward thelower retaining device 60. The flange 50 encircles the core 90. Theflange 50 has a radially inner surface 52 facing the core 90. Thesurface 52 extends radially outwardly from the concave surface 24 andtoward the lower retaining device 60. The surface 52 on the flange 50 isspaced from the core 90, as shown in FIG. 6, until a predetermined loadis applied to the apparatus 10.

The core 90 deflects toward the surface 52 on the flange 90 when a loadis applied to the apparatus 10 to move the upper and lower retainingdevices 20 and 60 relative to each other. When the predetermined load isapplied to the apparatus 10, as shown in FIG. 7, the core 90 deflectsinto engagement with the surface 52 on the flange 50. When the core 90engages the flange 50, the core stiffens since further deflection of thecore is restricted by the flange 50.

The surface 52 of the flange 50 may have any desired configuration. Thesurface 52 may have a first portion that extends closer to the core 90than a second portion so that the core engages the first portion of thesurface 52 prior to engaging the second portion of the surface 52.Accordingly, the core 90 may engage different portions of the surface 52as different loads are applied to the apparatus 10 to vary the stiffnessof the core at the different loads.

It is contemplated that the retaining member 21 may have an innersurface (not shown) extending from the concave inner surface 24 to theopening 36 and spaced from the core 90 until a predetermined load isapplied to the apparatus 10. When the predetermined load is applied tothe apparatus 10, the core 90 deflects into engagement with the innersurface (not shown) extending from the concave surface 24 to the opening36. When the core 90 engages the inner surface extending from theconcave surface 24 to the opening 36, the core stiffens since furtherdeflection of the core is restricted by the retaining member 21.

The lower retaining device 60 (FIGS. 1-2) is identical in configurationto the upper retaining device 20. The lower retaining device 60 includesa lower or second retaining member or ring 61 and a mounting member 100.The disc 18 includes the lower retaining member 61. The lower retainingmember 61 is identical to the upper retaining member 21. Accordingly,the lower retaining member 61 will not be described in detail. The lowerretaining member 61 is rigid and made from the same material as theupper retaining member 21, such as a titanium alloy. The lower retainingmember 61 has an outer surface 62 engageable with the vertebra 14. Aninner concave surface 64 of the lower retaining member 61 is affixed orbonded to the resilient core 90. It is contemplated that the innersurface 64 may have beads (not shown) sintered on the inner surface or atexture (not shown) etched onto the inner surface to help connect thelower retaining member 61 to the core 90.

A plurality of guides or ribs 66 (FIGS. 2 and 3) and a central rib 68extend from the outer surface 62. The lower retaining member 61 may haveany number of ribs 66. The ribs 66 engage the vertebra 14, as shown inFIGS. 6 and 7, to retain the apparatus 10 in position between thevertebrae 12 and 14. The outer surface 62 may also have beads (notshown) sintered on the outer surface or a texture (not shown) etchedonto the outer surface to further retain the apparatus 10 between thevertebrae 12 and 14.

The ribs 66 extend generally parallel to each other from the proximalside 30 of the disc 18 to the anterior side 32. The central rib 68 (FIG.2) extends from the anterior side 32 to an axially extending circularopening 70 in the lower retaining member 61. It is contemplated that theribs 66 and 68 may extend in any desired direction. The direction inwhich the ribs 66 and 68 extend is determined by the direction ofinsertion of the disc 18.

The axially extending opening 70 (FIG. 2) extends through the outersurface 62 and the inner surface 64 of the upper retaining member 61.The lower retaining member 61 has a frustoconical surface 71 at leastpartially defining the opening 70. A lower portion of the opening 70 hasa first diameter and an upper portion of the opening has a seconddiameter smaller than the first diameter. The opening 70 is centrallylocated between two of the ribs 66. Accordingly, there is no ribextending from the proximal side 30 of the disc 18 to the opening 70.Although the opening 70 is described as being circular, it iscontemplated that the opening may have any desired shape.

A flange portion 72 extends from the lower retaining member 61 on theanterior side 32 of the disc 18. The flange portion 72 has a recess 74adjacent the central rib 68. The recess 74 is defined by an uppersurface 76 and side surfaces 78 and 80 extending downwardly from theupper surface 76. An oval shaped slot 82 extends through the uppersurface 76 of the flange portion 72. The slot 82 extends in a directiontransverse to the direction in which the central rib 68 extends.

The inner concave surface 64 (FIG. 2) of the lower retaining member 61is affixed or bonded to the resilient core 90. The lower retainingmember 61 includes a peripheral flange portion 84 extending toward theupper retaining device 20. The flange 84 encircles the core 90. Theflange 84 has a radially inner surface 86 facing the core 90. Thesurface 86 extends radially outwardly from the concave surface 64 andtoward the upper retaining device 20. The surface 86 on the flange 84 isspaced from the core 90, as shown in FIG. 6, until a predetermined loadis applied to the apparatus 10.

The core 90 deflects toward the surface 86 on the flange 84 when a loadis applied to the apparatus 10 to move the upper and lower retainingdevices 20 and 60 relative to each other. When a predetermined load isapplied to the apparatus 10, as shown in FIG. 7, the core 90 deflectsinto engagement with the surface 86 on the flange 84. When the core 90engages the flange 84, the core stiffens since further deflection of thecore is restricted by the flange 84.

The surface 86 of the flange 84 may have any desired configuration. Thesurface 86 may have a first portion that extends closer to the core 90than a second portion so that the core engages the first portion of thesurface 86 prior to engaging the second portion of the surface 86.Accordingly, the core 90 may engage different portions of the surface 86as different loads are applied to the apparatus 10 to vary the stiffnessof the core at different loads. It is also contemplated that the flange84 on the lower retaining member 61 may engage the flange 50 on theupper retaining member 21 when a predetermined load is applied to theapparatus 10.

It is contemplated that the retaining member 61 may have an innersurface (not shown) extending from the concave inner surface 64 to theopening 70 and spaced from the core 90 until a predetermined load isapplied to the apparatus 10. When the predetermined load is applied tothe apparatus 10, the core 90 deflects into engagement with the innersurface (not shown) extending from the concave surface 64 to the opening70. When the core 90 engages the inner surface extending from theconcave surface 64 to the opening 70, the core stiffens since furtherdeflection of the core is restricted by the retaining member 61.

The resilient core 90 is one-piece and may be made of a urethanesilicone blend manufactured by the Polymer Technology Group located inBerkley, Calif. The resilient core 90 may be adhered or bonded to theupper and lower retaining members 21 and 61 in any manner known in theart. It is contemplated that the resilient core 90 could be insertmolded, transfer molded or injection molded between the upper and lowerretaining members 21 and 61. The core 90 may be molded between the upperand lower retaining members 21 and 61 by injecting the material for thecore through one of the openings 36 or 70 in the upper and lowerretaining members.

The resilient core 90 may be made of a polymer that is asilicone-polycarbonate-urethane copolymer by the name of CarboSil™manufactured by the Polymer Technology Group located in Berkley, Calif.The resilient core 90 is prepared through a multi-step bulk synthesisduring which polydimethylsiloxane is incorporated into the polymer softsegment with aliphatic, hydroxyl-terminated polycarbonate oligomers. Thehard segment consists of an aromatic diisocyanate with a low molecularweight glycol chain extender. The copolymer chains are terminated withsilicone.

The material of the resilient core 90 combines the biocompatibility andbiostability of silicone elastomers with the processibility andtoughness of thermoplastic urethane elastomers. The material of theresilient core 90 has a relatively high hard segment content thatsoftens significantly upon reaching equilibrium with the body of apatient. The relevant equilibrium involves thermal equilibrium with thebody at approximately 37° C. and equilibrium water and solute uptake bythe polymer after being implanted in the body. The material of theresilient core 90 has a decreased modulus at 37° C. compared to that atroom temperature. Accordingly, the higher durometer polymer can be usedfor its biostability, since conditions in the human body lower themodulus of the polymer to the desired range of compressive stiffness.

The resilient core 90 is wedge shaped. The upper retaining member 21 isspaced from the lower retaining member 61 a first distance adjacent theproximal side 30 of the disc 18. The upper retaining member 21 is spacedfrom the lower retaining member 61 a second distance greater than thefirst distance adjacent the anterior side 32 of the disc 18. It iscontemplated that the upper retaining member 21 may be spaced from thelower retaining member 61 by any desired distances.

The core 90 has an upper or first convex surface 92. The upper convexsurface 92 is affixed to the concave inner surface 24 of the upperretaining member 21. A lower or second convex surface 94 is affixed tothe concave inner surface 64 of the lower retaining member 61.

The core 90 includes a radially outer surface 96. Arcuate transitionsurfaces 98 extend between the radially outer surface 96 and the upperand lower surfaces 92 and 94. The radially outer surface 96 is spacedfrom the flanges 50 and 84 on the upper and lower retaining members 21and 61 until the predetermined load is applied to the apparatus 10.

The peripheral surface 96 and the transition surfaces 98 may have anydesired configuration. The surfaces 96 and 98 may have first portionsthat extend closer to the flanges 50 and 84 than second portions so thatthe first portions engage the flanges 50 and 84 prior to the secondportions. Accordingly, the different portions of the surfaces 96 and 98may engage the flanges 50 and 84 as different loads are applied to theapparatus 10 to vary the stiffness of the core 90 at different loads.

Each of the retaining devices 20 and 60 (FIGS. 1-7) includes a mountingmember 100 to help connect the disc 18 to the vertebrae 12 and 14. Themounting members 100 also help position the disc 18 between thevertebrae 12 and 14. The mounting members 100 (FIG. 6) extend into theopenings 36 and 70 in the retaining members 21 and 61 when the apparatus10 is connected to the vertebrae 12 and 14. The disc 18 is insertedbetween the vertebrae 12 and 14 after the mounting members 100 areconnected to the vertebrae. The ribs or guides 26 and 66 on oppositesides of the openings 36 and 70 of the disc 18 engage the mountingmembers 100 to guide the disc into a desired position between thevertebrae 12 and 14. The mounting members 100 are identical to eachother. Accordingly, only one mounting member 100 will be described indetail.

The mounting member 100 (FIG. 5) is rigid and made of a biocompatiblematerial such as a biocompatible metal or polymer. It is contemplatedthat the mounting member 100 could be made of a titanium alloy. Themounting member 100 has an outer surface 102 that faces the vertebra. Aninner concave surface 104 of the mounting member 100 faces the resilientcore 90. The inner concave surface 104 of the mounting member 100 of theupper retaining device 20 faces the upper surface 92 of the core 90. Theinner concave surface 104 of the mounting member 100 of the lowerretaining device 60 faces the lower surface 94 of the core 90.

The resilient core 90 deflects toward the concave surfaces 104 when aload is applied to the apparatus 10 to move the upper and lowerretaining devices 20 and 60 relative to each other. The core 90 deflectsinto the openings 36 and 70 in the upper and lower retaining members 21and 61 and into engagement with the concave surfaces 104 when the spine16 is subject to a predetermined load, as shown in FIG. 7. When the core90 engages the surfaces 104 of the mounting members 100, the resilientcore stiffens since further deflection of the core toward the retainingdevices 20 and 60 is restricted. It is contemplated that the retainingmember 100 may have an axially extending opening to permit the escape ofgas from between the core 90 and the mounting member.

The surfaces 104 of the mounting member 100 may have any desiredconfiguration. The core 90 may engage different portions of the surfaces104 as different loads are applied to the apparatus 10 to vary thestiffness of the core 90 at different loads. It is also contemplatedthat the surface 104 of the mounting member 100 of the retaining device20 may have a different configuration than the surface 104 of themounting member 100 of the retaining device 61.

Projections 106 extend from the outer surface 102 of the mounting member100. The projections 106 engage the vertebrae 12 and 14 to help retainthe apparatus 10 in position between the vertebra 12 and 14. Althoughthe mounting member 100 is shown having four projections 106, it iscontemplated that the mounting member may have any number ofprojections. It is contemplated that the projections 106 may have anydesired shapes, sizes, and/or tip configurations. The projections 106may include passages for bone ingrowth, have barbs, and/or have hooks.

The mounting member 100 includes a circular body 110 from which theprojections 106 extend. Although the body 110 of the mounting member 100is shown as being circular, it is contemplated that the body 110 mayhave any desired configuration that permits the mounting member 100 toslide into the openings 36 and 70 in the disc 18.

The body 110 of the mounting member 100 has a radially outerfrustoconical surface 112. A rounded transition surface 113 extends fromthe radially outer surface 112 to the concave surface 104. The body 110has a first diameter adjacent the outer surface 102 and a seconddiameter adjacent the transition surface 113 that is smaller than thefirst diameter. The radially outer surfaces 112 and/or the transitionsurfaces 113 of the mounting members 100 engage the ribs or guides 26and 66 on the retaining members 21 and 61 to guide movement of the disc18 in a first posterior direction relative to the mounting members andthe vertebrae 12 and 14. The central ribs 28 and 68 on the upper andlower retaining members 21 and 61 act as stops to prevent movement ofthe disc 18 in the first direction after the disc has been inserted to adesired depth. The central ribs 28 and 68 engage the radially outersurfaces 112 and/or the transition surfaces 113 on the mounting member100. When the central ribs 28 and 68 engage the mounting members 100,the radially outer surfaces 112 and/or the transition surfaces 113 guiderelative movement between the mounting members and the retaining members21 and 61 in second directions extending transverse to the firstdirections so that the mounting members move into the openings 36 and 70in the disc 18.

The radially outer frustoconical surfaces 112 on the mounting members100 engage the frustoconical surfaces 37 and 71 on the upper and lowerretaining members 21 and 61 when the mounting members are in theopenings 36 and 70 in the disc 18. The engagement of the surfaces 112with the surfaces 37 and 71 creates interference fits between themounting members 100 and the disc 18. Accordingly, the disc 18 isprevented from moving relative to the mounting members 100.

The radially outer surface 112 has four recesses 114, two of which areshown in FIG. 5. The recesses 114 are located at 90° relative to eachother. Although the mounting member 100 is described as having fourrecesses 114, it is contemplated that the mounting member 100 may haveany number of recesses.

The mounting members 100 may be connected to the vertebrae 12 and 14using a surgical tool that includes an actuator 120 and a pair ofinsertion members 140 (FIGS. 8 and 9). The mounting members 100 areconnected to the members 140 and the actuator 120 moves the members awayfrom each other to connect the mounting members to the vertebrae. Theactuator 120 (FIG. 8) may be a modular spine distractor manufactured byFriedrich GmbH of Solingen, Germany to which the members 140 areconnected. The actuator 120 is known in the art and will not bedescribed in detail.

The actuator 120 includes a pair of actuation handles 122 and a pair ofseparators 124 that are connectable to the members 140. The handles 122are connected to the separators 124 by a linkage system 126. Uponmovement of the handles 122 toward each other, the linkage system 126causes the separators 124 to move away from each other. The actuator 120also includes a locking mechanism 128 for locking the separators 124 ata desired distance from each other.

The insertion members 140 (FIGS. 9-13) are connectable to the separators124. The members 140 are identical to each other. Accordingly, only onemember 140 will be described in detail.

The member 140 includes a connecting end 144 that is insertable into anopening (not shown) in one of the separators 124 of the actuator 120.The end 144 includes a pair of projections 146. The projections 146(FIG. 12) extend generally parallel to each other and define a channel148 between them. The end 144 is inserted into the opening (not shown)in the separator 124 of the actuator 120 to connect the member 140 tothe actuator in a known manner. The member 140 may be removed from theseparator 124 in a known manner. It is contemplated that the end 144 ofthe member 140 hay have any desired configuration to connect the memberto a desired actuator.

The projections 146 (FIGS. 9-12) extend from a first end 150 of acentral body 152 of the member 140. The central body 152 has an uppersurface 154 and a parallel lower surface 156 extending from the firstend 150 to a second end 158 of the central body. The projections 146extend at an angle to the surfaces 154 and 156. It is contemplated thatthe projections 146 may extend at any desired angle to the surfaces 154and 156. The upper surface 154 has a scalloped recess 164.

Side surfaces 160 and 162 extend from the upper surface 154 to the lowersurface 156. A pair of longitudinally extending grooves 166 (FIG. 10)located in the side surfaces 160 and 162 extend along the body 152. Thegrooves 166 extend from the first end 150 to the second end 158.

A slider 168 (FIGS. 9 and 14) may be connected to the body 152 of themember 140. The slider 168 engages one of the vertebrae 12 and 14 toprevent further insertion of the mounting members 100 in the proximaldirection between the vertebrae. The slider 168 includes a main bodyportion 170 with a threaded opening 172. A pair of flanges 174 extenddownwardly from the body portion 170. The flanges 174 (FIG. 14) extendgenerally parallel to each other and include portions 176 extendingtoward each other. The portions 176 are received in the grooves 166 inthe body 152 of the member 140. The slider 168 includes a verticallyextending groove 178 in a surface 179 that faces away from theconnecting end 144 of the member 140.

The slider 168 may be moved relative the body 152 toward and away fromthe end 144 of the member 140. A set screw (not shown) is threaded intothe opening 172 and extends into the scalloped recess 164 to preventmovement of the slider 168 relative to the body 152. The scallopedrecess 164 defines a plurality of positions for the slider 168 relativeto the member 140.

An insertion end 180 (FIGS. 9-13) of the member 140 extends from thesecond end 158 of the body 152. The insertion end 180 extends at anangle to the upper and lower surfaces 154 and 156 of the body 152 andgenerally parallel to the projections 146. It is contemplated that theinsertion end 180 may extend at any desired angle relative to thesurfaces 154 and 156. The insertion end 180 (FIG. 11) has a lowersurface 182 that extends at an angle to the lower surface 156 of thebody 152.

The insertion end 180 (FIG. 12) includes a recess 184 for receiving themounting member 100. The recess 184 is generally U-shaped with an openend 186 through which the mounting member 100 may be inserted into therecess and removed from the recess. The recess 184 is defined bysidewalls 188 and 190 interconnected by a back wall 192. A bottom wall194 extends generally perpendicular to the sidewalls 188 and 190 and theback wall 192.

The sidewall 188 has a notch 198 extending radially outwardly. Thesidewall 190 includes a notch 200 extending radially outwardly. The backwall 192 has a notch 202 extending toward the body 152. A groove 206(FIGS. 10 and 13) is formed in the sidewall 188 extending from adjacentthe open end 186 to the notch 198. A groove 208 extends from the notch198 to the notch 202. A groove (not shown) similar to the groove 208extending between the notch 202 and the notch 200 is formed in thesidewall 190. Another groove (not shown) similar to the groove 206extending from the notch 200 to adjacent the open end 186 is formed inthe sidewall 190.

A first circular opening 216 extends through the bottom wall 194 and iscentrally located in the recess 184. The opening 216 permits removal ofthe mounting member 100 from the recess 184 if needed. A second smallercircular opening 218 extends through the bottom wall 194 and is locatedin the notch 202.

A spring member 230 (FIGS. 9 and 15) is received in the recess 184 tohold the mounting member 100 in the recess. The spring member 230 isgenerally U-shaped and includes a pair of arms 232 and 234 extendingfrom a base 236. A projection 238 extends from the base 236 in adirection opposite from the arms 232 and 234. The projection 238 has acircular opening 240 for receiving a pin (not shown) to connect thespring member 230 to the member 140. The pin (not shown) extends throughthe opening 240 in the spring member 230 and into the opening 218 in themember 140 to connect the spring member to the member 140.

The arm 232 includes an upwardly extending end 246 that engages themounting member 100 to retain the mounting member in the member 140. Theend 246 has a radially inwardly extending projection 248. The projection248 extends into one of the recesses 114 in the mounting member 100 toretain the mounting member in the member 140.

The arm 234 has an upwardly extending end 252. The end 252 has aradially inwardly extending projection 254. The projection 254 extendsinto one of the recesses 114 in the mounting member 100 to retain themounting member in the member 140.

The spring member 230 is inserted into the recess 184 through the openend 186. The arms 232 and 234 extend into the groove 206 in the sidewall188 and the groove (not shown) in the sidewall 190 extending from thenotch 200 to adjacent the open end 186, as the spring 230 is beinginserted into the recess 184. The ends 246 and 252 of the arms 232 and234 move toward each other. When the ends 246 and 252 are adjacent thenotches 198 and 200, the ends 246 and 252 move away from each other.

When the spring 230 (FIG. 9) is inserted in the recess 184, the arm 232extends into the groove 208 and the arm 234 extends into the groove (notshown) extending from the notch 202 to the notch 200 in the insertionend 180 of the member 140. The opening 240 in the projection 238 of thespring member 230 is aligned with the opening 218 in the insertion end180. A pin (not shown) extends through the opening 240 in the springmember 230 and into the opening 218 to retain the spring member in therecess 184. The ends 246 and 252 extend upwardly into the notches 198and 200 in the sidewalls 188 and 190.

Upon insertion of the mounting member 100 between the ends 246 and 252of the spring 230, the ends move radially outwardly away from each otherinto the notches 198 and 200 until the recesses 114 are aligned with theprojections 248 and 254. When the recesses 114 are aligned with theprojections 248 and 254, the ends 246 and 252 move toward each otherinto the recesses to retain the mounting member 100 in the insertion end180. The mounting member 100 may be removed from the recess 184 byovercoming the retaining force applied by the spring member 230.

An insertion tool 300 for inserting the disc 18 between the vertebrae 12and 14 after the mounting members 100 are connected to the vertebrae 12and 14 is illustrated in FIGS. 16 and 17. The tool 300 (FIG. 16)resembles a common pair of scissors and has a pair of legs 302 and 304pivotally connected to one another. The tool 300 includes a grasping end306 formed by a pair of jaws 308 on the legs 302 and 304. The jaws 308(FIG. 17) include oval shaped projections 310 extending toward eachother. The projections 310 are inserted into the openings 48 and 82 inthe disc 18 to grasp the disc for insertion between the vertebrae 12 and14.

The leg 302 (FIG. 15) has an enlarged end 312 opposite the jaw 308. Theenlarged end 312 may be struck with a mallet to drive the disc 18between the vertebrae 12 and 14 if needed. The leg 304 has a curvedhandle 314 opposite the jaw 308. The handle 314 is easily grasped by asurgeon for manipulating the tool 300.

A locking mechanism 320 prevents the jaws 308 from pivoting away fromeach other after the projections 310 have been inserted into theopenings 48 and 82 in the disc 18. The locking mechanism 320 includes arod 322 pivotally connected to a mounting portion 324 extending from theleg 304. The rod 322 has a threaded end 326 that extends through anopening 328 in the leg 302. A nut 332 threadably engages the end 326 ofthe rod 322 and engages the leg 302 to prevent the jaws 308 frompivoting away from each other.

When the apparatus 10 is to be inserted between the vertebrae 12 and 14,an anterior space adjacent the vertebrae is exposed using aretroperitoneal or transperitoneal approach. A midline reference isestablished. A midline marker, such as a K-wire, is placed to maintain areference point to the center of one of the vertebrae 12 and 14. Thespace between the vertebrae 12 and 14 is distracted and the damaged discbetween the vertebrae is excised. After the damaged disc is excised, thecartilaginous end plates are removed from the vertebrae 12 and 14. Thevertebrae 12 and 14 are then sculpted as desired.

The appropriate size apparatus 10 is determined by using trial sizers.The trial sizers are similar to the disc 18. The trial sizers areinserted between the vertebrae 12 and 14 to determine the desiredfootprint, wedge angle, and disc height needed to replace the exciseddisc. The desired footprint, wedge angle and disc height are confirmedusing fluoroscopy.

The mounting members 100 are then inserted into the vertebrae 12 and 14.The appropriate members 140 are selected based upon the desired wedgeangle for use between the vertebrae 12 and 14. The mounting members 100are inserted into the recesses 184 in the member 140. The insertion ends180 of the members 140 are inserted between the vertebrae 12 and 14until the midline marker extends into the groove 178 on the slider 168and the slider 168 engages the anterior ridge of one of the vertebrae 12and 14 directly under the midline marker. Once the insertion ends 180 ofthe members 140 have been inserted into the desired depth, the insertionends are moved away from each other by the actuator 120 to insert theprojections 106 on the mounting members 100 into the vertebrae 12 and14. After the mounting members 100 have been connected to the vertebrae12 and 14, the members 140 are removed from between the vertebrae 12 and14 leaving the mounting members behind.

After the mounting members 100 are connected to the vertebrae 12 and 14,a trial sizer may be reinserted between the vertebrae. Verification ofthe position of the trial sizer is achieved using fluoroscopy. If it isdetermined that the mounting members 100 are not in the desiredpositions, the mounting members can be easily removed and repositionedin the vertebrae.

After the mounting members 100 are connected to the vertebrae 12 and 14in their desired positions, the insertion tool 300 is connected with thedisc 18. The disc 18 is then inserted between the vertebrae 12 and 14.During insertion of the disc 18, the ribs 26 and 66 on opposite sides ofthe openings 36 and 70 engage the surfaces 112 and 113 on the mountingmembers 100 to guide insertion of the disc. The central ribs 28 and 68engage the mounting members 100 when the disc 18 has been inserted tothe desired depth between the vertebrae 12 and 14. The ribs 26, 28, 66,and 68 on the disc 18 guide insertion of the mounting members 100 intothe openings 36 and 70 in the disc 18.

After the disc 18 is placed into the desired position between thevertebrae 12 and 14, the tool 300 is removed from the disc. The ribs 26,28, 66 and 68 on the disc 18 engage the vertebrae 12 and 14 when themounting members 100 are inserted in the openings 36 and 70 in the disc18. The mounting members 100 and ribs 26, 28, 66 and 68 retain theapparatus 10 in position between the vertebrae 12 and 14.

When the apparatus 10 is in use in the spinal column 16, the upperretaining device 20 is affixed to the vertebra 12. The ribs 26 and 28and the projections 106 on the mounting member 100 resist relativemovement between the upper retaining device 20 and vertebra 12. Thelower retaining device 60 is affixed to the vertebra 14. The ribs 66 and68 and the projections 106 on the mounting member 100 resist relativemovement between the lower retaining device 60 and the vertebra 14.

When the upper and lower retaining devices 20 and 60 move relative toeach other, such as when the spine 16 is in compression, as shown inFIG. 7, the resilient core 90 deflects toward the concave surfaces 104on the mounting members 100. The resilient core 90 also deflects towardthe surfaces 52 and 86 on the retaining members 21 and 61 when a load isapplied to the apparatus. Accordingly, the core 90 expends energy toreduce stress in the core upon relative movement of the upper and lowerretaining devices 20 and 60 to provide a relatively long fatigue lifefor the apparatus 10.

The resilient core 90 deflects into engagement with the surfaces 104 ofthe mounting members 100 when a predetermined load is applied. The core90 also deflects into engagement with the surfaces 52 and 86 on theretaining members 21 and 61 when a predetermined load is applied.Accordingly, the core 90 stiffens when the core engages the surfaces104, 52, and 86 since further deflection of the core is restricted. Itis contemplated that the core 90 may engage the surfaces 104, 52, and 86at different applied loads.

Although the ribs 26 and 66 on the disc 18 are described as engaging themounting members 100 to guide insertion of the disc between thevertebrae 12 and 14, it is contemplated that the mounting members 100may have grooves that ribs on the disc 18 extend into to guide insertionof the disc. It is also contemplated that the mounting members 100 mayhave ribs that extend into grooves in the disc 18 to guide insertion ofthe disc. Furthermore, it is contemplated that the disc 18 may beinserted between the vertebrae 12 and 14 without use of the mountingmembers 100. If the disc 18 is used without the mounting members 100, itis contemplated that the retaining members 21 and 61 of the retainingdevices 20 and 60 would include inner concave surfaces similar to theinner concave surfaces 104 of the mounting members. The core 90 would bespaced from the inner concave surfaces on the retaining members 21 and61 and deflect into engagement with the inner concave surfaces when apredetermined load was applied to the apparatus 10.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims. The presentlydisclosed embodiments are considered in all respects to be illustrative,and not restrictive. The scope of the invention is indicated by theappended claims, rather than the foregoing description, and all changesthat come within the meaning and range of equivalence thereof areintended to be embraced therein.

1. A method for replacing a damaged spinal disc between first and secondvertebrae of a spinal column comprising: connecting a first mountingmember with the first vertebra of the spinal column; and moving anartificial disc between the first and second vertebrae and intoengagement with the first mounting member to guide the artificial discinto position between the first and second vertebrae, the artificialdisc including a resilient core having a first surface and a secondsurface, a first retaining member fixedly connected to the first surfaceof the resilient core, and a second retaining member fixedly connectedto the second surface of the resilient core, the first retaining memberhaving an outer surface directly engageable with the first vertebra ofthe spinal column after the artificial disc is in position between thefirst and second vertebrae and an inner surface facing the first surfaceof the resilient core, the second retaining member having an outersurface directly engageable with the second vertebra of the spinalcolumn after the artificial disc is in position between the first andsecond vertebrae and an inner surface facing the second surface of theresilient core.
 2. A method as defined in claim 1 further includingengaging the first mounting member with a guide on the first retainingmember to guide movement of the first retaining member into positionbetween the first and second vertebrae.
 3. A method as defined in claim2 wherein said step of engaging the first mounting member with the guideon the first retaining member includes engaging the first mountingmember with a guide extending from the outer surface of the firstretaining member and engaging the first vertebra with the guide.
 4. Amethod as defined in claim 1 further including engaging the firstmounting member with first and second guides extending generallyparallel to each other on the first retaining member to guide movementof the first retaining member into position between the first and secondvertebrae.
 5. A method as defined in claim 1 further including engagingthe first mounting member with a stop on the first retaining member toprevent relative movement between the first retaining member and thefirst mounting member in a first direction.
 6. A method as defined inclaim 5 further including guiding movement of the first retaining memberrelative to the first mounting member in a second direction extendingtransverse to the first direction.
 7. A method as defined in claim 1further including guiding movement of the first mounting member into anopening in the first retaining member.
 8. A method as defined in claim 1wherein the step of connecting the first mounting member with the firstvertebra includes engaging the first mounting member with a surgicaltool for connecting the first mounting member to the first vertebra. 9.A method as defined in claim 8 wherein the step of engaging the firstmounting member with the surgical tool includes extending a portion ofthe surgical tool into a recess in the first mounting member.
 10. Amethod as defined in claim 1 further including spacing an inner surfaceof the first mounting member that faces the core from the core.
 11. Amethod as defined in claim 1 further including connecting the artificialdisc to the first mounting member.
 12. A method as defined in claim 11wherein the step of connecting the artificial disc to the first mountingmember includes preventing movement of the first mounting memberrelative to the artificial disc.
 13. A method as defined in claim 12wherein the step of preventing movement of the first mounting memberrelative to the artificial disc includes connecting the artificial discto the first mounting member with an interference fit.
 14. A method asdefined in claim 13 wherein the step of connecting the artificial discto the first mounting member with an interference fit includes engaginga frustoconical surface on the artificial disc with a frustoconicalsurface on the first mounting member.
 15. A method as defined in claim 1further including connecting a second mounting member to the secondvertebra, said step of moving the artificial disc between the first andsecond vertebrae including engaging the second mounting member with theartificial disc to guide movement of the artificial disc into positionbetween the first and second vertebrae.
 16. A method as defined in claim15 further including engaging the first mounting member with a firstguide on the first retaining member to guide movement of the firstretaining member into position between the first and second vertebraeand engaging the second mounting member with a second guide on thesecond retaining member to guide movement of the second retaining memberinto position between the first and second vertebrae.
 17. A method asdefined in claim 16 wherein the step of engaging the first mountingmember with the first guide on the first retaining member includesengaging the first mounting member with the first guide extending fromthe outer surface of the first retaining member and engaging the firstvertebra with the first guide, the step of engaging the second mountingmember with the second guide on the second retaining member includingengaging the second mounting member with the second guide extending fromthe outer surface of the second retaining member and engaging the secondvertebra with the second guide.
 18. A method as defined in claim 15further including engaging the first mounting member with first andsecond guides extending generally parallel to each other on the firstretaining member to guide movement of the first retaining member intoposition between the first and second vertebrae, and engaging the secondmounting member with third and fourth guides extending generallyparallel to each other on the second retaining member to guide movementof the second retaining member into position between the first andsecond vertebrae.
 19. A method as defined in claim 15 further includingengaging the first mounting member with a first stop on the firstretaining member to prevent relative movement between the firstretaining member and the first mounting member in a first direction andengaging the second mounting member with a second stop on the secondretaining member to prevent relative movement between the secondretaining member and the second mounting member in the first direction.20. A method as defined in claim 19 further including guiding movementof the first retaining member relative to the first mounting member in adirection extending transverse to the first direction and guidingmovement of the second retaining member relative to the second mountingmember in a direction extending transverse to the first direction.
 21. Amethod as defined in claim 15 further including guiding movement of thefirst mounting member into an opening in the first retaining member andguiding movement of the second mounting member into an opening in thesecond retaining member.
 22. A method as defined in claim 15 wherein thestep of connecting the first mounting member with the first vertebraincludes connecting the first mounting member with a surgical tool forconnecting the first mounting member to the first vertebra, the step ofconnecting the second mounting member with the second vertebra includingconnecting the second mounting member with the surgical tool forconnecting the second mounting member to the second vertebra.
 23. Amethod as defined in claim 22 further including moving the first andsecond mounting members away from each other to connect the first andsecond mounting members to the first and second vertebrae.
 24. A methodas defined in claim 22 wherein the step of connecting the first mountingmember with the surgical tool includes extending a first portion of thesurgical tool into a recess in the first mounting member, the step ofconnecting the second mounting member with the surgical tool includingextending a second portion of the surgical tool into a recess in thesecond mounting member.
 25. A method as defined in claim 15 furtherincluding spacing an inner surface of the first mounting member thatfaces the core from the core and spacing an inner surface of the secondmounting member that faces the core from the core.
 26. A method asdefined in claim 15 further including connecting the artificial disc tothe first and second mounting members.
 27. A method as defined in claim26 wherein the step of connecting the artificial disc to the first andsecond mounting members includes preventing movement of the first andsecond mounting members relative to the artificial disc.
 28. A method asdefined in claim 27 wherein the step of preventing movement of the firstand second mounting members relative to the artificial disc includesconnecting the artificial disc to the first and second mounting memberswith interference fits.
 29. A method as defined in claim 28 wherein thestep of connecting the artificial disc to the first and second mountingmembers with interference fits includes engaging frustoconical surfaceson the artificial disc with frustoconical surfaces on the first andsecond mounting members.
 30. A method as defined in claim 1 wherein thestep of moving the artificial disc between the first and secondvertebrae includes connecting a surgical tool to a first portion of thefirst retaining member.
 31. A method as defined in claim 30 wherein thestep of moving the artificial disc between the first and secondvertebrae includes connecting the surgical tool to a first portion ofthe second retaining member.
 32. A method as defined in claim 31 whereinthe step of connecting the surgical tool to the first portion of thefirst retaining member includes extending a first portion of thesurgical tool into a first opening in the first portion of the firstretaining member.
 33. A method as defined in claim 32 wherein the stepof connecting the surgical tool to the first portion of the secondretaining member includes extending a second portion of the surgicaltool into a first opening in the first portion of the second retainingmember.
 34. A method for replacing a damaged spinal disc between firstand second vertebrae of a spinal column comprising: connecting a firstmounting member with the first vertebra of the spinal column; moving anartificial disc between the first and second vertebrae and intoengagement with the first mounting member to guide the artificial discinto position between the first and second vertebrae, the artificialdisc including a resilient core having a first surface and a secondsurface, a first retaining member connected to the first surface of theresilient core, and a second retaining member connected to the secondsurface of the resilient core, the first retaining member having anouter surface engageable with the first vertebra of the spinal columnand an inner surface facing the first surface of the resilient core, thesecond retaining member having an outer surface engageable with thesecond vertebra of the spinal column and an inner surface facing thesecond surface of the resilient core; and engaging the first mountingmember with a guide extending from the outer surface of the firstretaining member to guide movement of the first retaining member intoposition between the first and second vertebrae and engaging the firstvertebra with the guide.
 35. A method as defined in claim 34 furtherincluding engaging the first mounting member with first and secondguides extending generally parallel to each other on the first retainingmember to guide movement of the first retaining member into positionbetween the first and second vertebrae.
 36. A method as defined in claim34 further including connecting a second mounting member to the secondvertebra, said step of moving the artificial disc between the first andsecond vertebrae including engaging the second mounting member with theartificial disc to guide movement of the artificial disc into positionbetween the first and second vertebrae.
 37. A method as defined in claim36 further including engaging the second mounting member with a secondguide on the second retaining member to guide movement of the secondretaining member into position between the first and second vertebrae.38. A method as defined in claim 37 wherein the step of engaging thesecond mounting member with the second guide on the second retainingmember includes engaging the second mounting member with the secondguide extending from the outer surface of the second retaining memberand engaging the second vertebra with the second guide.
 39. A method asdefined in claim 36 further including engaging the first mounting memberwith first and second guides extending generally parallel to each otheron the first retaining member to guide movement of the first retainingmember into position between the first and second vertebrae, andengaging the second mounting member with third and fourth guidesextending generally parallel to each other on the second retainingmember to guide movement of the second retaining member into positionbetween the first and second vertebrae.